Various endocrine disrupting chemicals (EDCs) such as bisphenol A (BPA), alkylphenols (4-nnonylphenol (NP) and 4-octylphenol (OP) and isobutylparaben (IBP) are a constant concern due to their widespread distribution. It has been reported that some combinations of honnone disrupting chemicals are much more powerful than any of the chemicals alone. In this study, the authors measured the expression of some estrogenic biomarker genes as Calbindin D9k (CaBP-9k), Progesterone receptor (PR), and Estrogen receptor alpha (ERa) to evaluate the individual or combinative estrogenic activity of BP A, NP, OP, and IBP in rat pituitary GH3 cell line. Most doses of the individual compounds and all doses of the combined chemicals significantly increased CaBP-9k and PR mRNA and protein expression compared to vehicle (VE). Interestingly, high doses (10 exponent-6 M and 10 exponent-5 M) of the EDCs combinations increased both translational and transcriptional levels of CaBP-9k up to 1.3 to 2.4 fold compared to doses of each individual EDCs. However, it has not found a significant difference in ERa mRNA and protein expression when a single chemical exposed. Taken together, the authors concluded that combinations of BPA, NP, OP, and IBP in rat pituitary GH3 cells had synergistic estrogenic activities on some estrogenic biomarker genes.